الفهرس 
Gross anatomy of the StomachOnly 14 pages are availabe for public view
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Abstract
Virtual endoscopy is an emerging technique in radiology developed in the past decade .It is a computer-generated simulation of the endoscopic perspective obtained by processing computed tomography (CT) and is one of the applications of virtual reality in medicine . Initial works were oriented to demonstrate the feasibility of the technique in the exploration of the entire human body, but soon focused experiences were carried out for specific clinical problems.
Recent advances in CT technology, 3D imagingsoftware, and cheaper data storage capacity havemade faster, simpler, and more accurate gastricimaging available. Two-dimensional MPR andCT gastrography, including virtual gastroscopyand transparency rendering, provide multiplane cross-sectional imaging, gastroscopic viewing,and UGIS imaging in the same data acquisition.They are also helpful in the detection and evaluationof gastric malignancies and a variety of inflammatoryconditions that affect the stomach(Kim JH et al, 2006).
Two-dimensional MPR provides accuratestaging of gastric cancer and extraluminal informationsuch as the presence of lymphadenopathyand distant metastasis. The ability to visualize anabnormality in multiple planes increases confidenceand helps better characterize the lesion(Kim JH et al, 2006).
When compared to axial 2D CT, virtual endoscopy has the advantage of displaying gastric lesions as they are seen with conventional gastroscopy, thus allowing an accurate categorization. When compared to conventional endoscopy, virtual CT gastroscopy is a noninvasive technique that enables a more accurate evaluation of lesion with simultaneous availability of endoscopic, multiplanar, and axial 2D images at the same time, local staging of gastric lesions, including the depth of parietal and perivisceral extension and the detection of lymph node and distant metastasis ( Kim et al., 2003 )
Conventional endoscopy is the established primary diagnostic investigation for patients suspected to have gastric lesions. Simplicity, availability, rapid evaluation, and relatively low cost are advantages offered by it. The ability to determine the exact location of the lesion, to appreciate its gross morphology and subtle color changes caused by inflammation, The ability to obtain biopsy specimens and to evaluate the stomach, the esophagus and the duodenum for synchronous lesions are added advantages. However, conventional endoscopy has limited value for accurate staging of the gastric cancer especially the determination of depth of infiltration and does not contribute to nodal staging. (Bhandari S, et al, 2004).
Endoscopic US also allows differentiationof mucosal from submucosal lesions and intramurallesion from extrinsic compression. Themain disadvantage of endoscopic US is that it isoperator dependent. In the evaluation of gastric cancer, multiple views must be obtained. EndoscopicUS also has limitations for the evaluationof distant lymphadenopathy and metastasis(Kim JH et al, 2006).
Recent advances in CT technology and 3Dimaging software enable us to obtain moredetailed gastric images. Virtual gastroscopy isa promising method for detecting EGC despiteits limitations. The advantages of virtualgastroscopy are that it has a wider field ofview than conventional gastroscopy, the angleof the virtual camera can be adjusted omnidirectionally,and it has no blind point becauseretrospective reconstruction is available(Kim JH et al., 2007)
Evaluation of gastric tumors and other abnormalities is possible with virtual endoscopic techniques using CT. Accurate evaluation of endoluminal morphology requires conventional endoscopy. Although it is invasive and has a limited field of view. Virtual endoscopy using 3D CT data sets provides an overview of tumors within the lumen of the gastrointestinal tract. Furthermore, extraluminal information can be obtained with 3D CT data sets.(Ogata, 1999)
Virtual gastroscopy was recently introduced as a potential diagnostic tool for the detectionof EGC. Virtual gastroscopy usingMDCT showed excellent results in the detection of EGC. The diagnostic performancefor overall lesion detection in patientswith EGC was significantly higher withvirtual gastroscopy than with 2D axial CT(Kim JH et al, 2007).
Detectionrate of patients with EGC was 69% using2D axial CT, 80% using 2D MPR, and 96%using virtual gastroscopy. According to that, virtual gastroscopy has great value for the detection of EGC (Kim JH et at., 2005).
The weakness ofvirtual gastroscopy lies in the detection of superficialflat lesions (type IIb) and lesions at the gastric angle and that virtual gastroscopyhas no advantage over 2D axial CT in the diagnosisof these types of EGC lesions(Kim JH et al., 2007).
Virtual gastroscopy is not a competitor for, but a complement of conventional endoscopy. Despite its limitations virtual gastroscopy is promising method for evaluation of gastric lesions accurately in combination with axial CT images and as complementary method to gastroscopy. With more technical developments in hardware and software some of above limitations may be solved in future. (Ogata et al., 1999).
CT gastrography including virtual gastroscopy is a promising method for evaluating gastric lesions despite its limitations. 2D-MPR and CT gastrography including virtual gastroscopy and transparency rendering can provide the comprehensive information from a single data acquisition for various gastric diseases, which otherwise would be obtained only by performing four different examinations including gastroscopy, UGIS, endoscopic US, and CT; however, further studies are required to prove the accuracy, efficacy, and cost effectiveness of virtual gastroscopy.(Kim JH, et al, 2006)
In conclusion, 3D-MDCT along with Virtual gastroscopy and MPR is a useful diagnostic modality for the pre-operative evaluation of patients with gastric cancer. With further technologic improvements in computer hardware and software including the development of scanners with greater resolution the capabilities of Virtual gastroscopy for the noninvasive evaluation of gastric cancer can be further enhanced.(Bhandari S. et al, 2004)